Chemical composition and sensory analysis of fresh pineapple juice and
deacidified pineapple juice using electrodialysis
Masniza Sairi*, Law Jeng Yih and Mohamad Roji Sarmidi
Department of Bioprocess Engineering, Faculty of Chemical and Natural Resources
Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor,
Malaysia
Abstract
Electrodialysis with monopolar ion exchange membranes was used to reduce
the acid content of pineapple juice. It is an electrochemical membrane separation
process in which electrically charged membranes and an electrical potential
difference are used to separate ionic species in the pineapple juice from other
uncharged components. Several physico-chemical (pH, titratable acidity and soluble
solids) and chemical (elemental contents) characteristics and sensory attributes
(sweetness, tartness, colour, odour and acceptability) of fresh pineapple juice and
deacidified pineapple juice were studied. Electrodialysis of pineapple juice resulted in
the reduction of titratable acidity. However there was a pH reduction in the diluting
stream. The transfer of the acids salts through the membrane along with the weak
acids disturbed the buffer action and resulting in the reduction of pH along with
reduction in acidity. The soluble solids content was unchanged. Result from
elemental analysis showed that the major mineral components in pineapple juice
(magnesium, phosphorus and potassium) were reduced in the diluting stream
compared to fresh juice. The result of sensory analysis of the deacidified pineapple
juice showed considerable increased in sweetness and reduction in the tartness. No
significant changes were observed in odour and colour.
Keywords: pineapple juice; electrodialysis; deacidification; chemical composition;
sensory analysis
_____________________________________________________________________
1. Introduction
1.1. Pineapple
Pineapple (Ananas comosus) is sometimes called the ‘King of Fruit’1.
Pineapple is grown extensively in Hawaii, Philippines, Caribbean area, Malaysia,
Taiwan, Thailand, Australia, Mexico, Kenya and South Africa. Pineapple has long
been one of the most popular of the non-citrus tropical and subtropical fruits, largely
because of its attractive flavour and refreshing sugar-acid balance2. It is available
fresh, canned and as juice1. 100 g pineapple contain 47-52 calories, 85.3-87.0 g water,
0.4-0.7 g protein, 0.2-0.3 g fat, 11.6-13.7 g total carbohydrate, 0.4-0.5 g fibre, 0.3-0.4
g ash, 17-18 mg calcium, 8-12 mg phosphorus, 0.5 mg iron, 1-2 mg sodium and 125-
•
Corresponding author: Tel.: +60-7-5535623 *Email: mas_nizam@yahoo.com
146 mg potassium3. Pineapple also contains 12-15 % sugars of which two-third is in
the form of sucrose and the rest are glucose and fructose. 0.6-1.2 % of pineapple is
acid of which 87 % is citric acid and 13 % is malic acid4,5. The pH of pineapple is
acidic, which is 3.71 and the acidity percentage is 53.5 %. The composition of the
juice varies with geographical, cultural and seasonal harvesting and processing.
About 10-25 % pineapple juice obtained from canning industry is not suitable
for production of single strength or concentrate juice, due to the high acidity5. Several
methods have been attempted in order to reduce the sourness by adding sweetening
agents, simple neutralization by alkali or partially remove it by ion-exchange
techniques6. There is an increasing demand for fruit juices with the original
characteristics of the fresh fruits and free from chemical additives. This results in the
search of new technologies that are able to improve the sensorial, nutritional and
microbiological quality of the fruit juices7. Since thermal processes largely affect the
characteristics of fruit juices, electrodialysis can be used as alternative to fruit juice
preservation and conservation, because it does not involve the use of heat treatment.
As such the nutritional quality and the sensorial attributes of the products are retained.
Hence a study is warranted to produce pineapple juices with acceptable acidity
level using an electrodialyzer system.
1.2. Electrodialysis and Ion Exchange Membrane
Electrodialysis is an electrochemical separation process by which ionic
(electrically charged) species are transported from one solution to another by crossing
one or more selective permeability membranes, under the influence of a direct
electrical current8. It also can be used to separate ionic species from uncharged
components. Electrodialysis is one of a group of membrane based separation
technologies that are finding increasing use in the agri-food industries. The
applications vary from demineralisation of cane sugar, desalination of cheese whey,
deacidification of fruit juices, wines stabilization, production of acids and bases from
a salt stream and for the recovery of concentrated acids.
The ion exchange membranes become the key element to electrodialysis
process. It is made of polymer matrix material with fixed charged groups covalently
bonded to the polymer matrix9. A membrane containing fixed negative charges is
called a cation exchange membrane; meanwhile a membrane with fixed positive
charges is referred as anion exchange membrane10.
2. Materials and methods
2.1. Preparation of pineapple juice
Fresh pineapple (Ananas comosus) was procured locally. The crown and stem
portions were removed and the skin was peeled using knife. After that, the fruit was
sliced and the fruit slices were pressed in a fruit juicer for one to two minutes11 to get
the pineapple juice. The pineapple juice was kept in a cold room at 4 °C.
2.2. Electrodialysis of pineapple juice
The volume of pineapple juice used was 1000 ml in each bottle solution. The
experimental set-up for deacidification of pineapple juice using electrodialysis is
shown in Figure 1. In the experiment, AFN and CMX membranes, which were
supplied by Tokuyama Soda Corp., Japan were used. The current density throughout
the system was maintained at 2.60 mA/cm2. In the electrode compartments, a 500 ml
of 5.0 % (w/v) sodium sulphate (Na2SO4) solution (Merck, analytical grade) was
used. The flow rate in the diluate and concentrate compartments was maintained at
500 ml/min. This study was carried out at room temperature.
Figure 1: The schematic diagram of membranes arrangement in the five-compartment
electrodialysis cell
During the electrodialysis processing, the pH of pineapple juice in the diluate
compartments was noted. Samples of pineapple juice from diluting stream and
concentrating stream were taken at 60 minutes interval for the determination of
titratable acidity and total soluble solids. For the determination of pineapple juice
elemental components, samples from diluting stream and concentrating stream were
collected after two hours of processing.
2.3. Analytical procedures
Analytical procedures carried out in this study were the analysis of titratable
acidity by titration method, pH, total soluble solids and elemental components by
ICP-MS.
2.4. TitratableaAcidity of pineapple juice
The pineapple juice contains a number of organic acids such as malic acid and
citric acid, which are readily neutralized by strong bases and can be titrated against
standard bases such as sodium hydroxide.
A 10 g sample of pineapple juice was weighed. Then, the sample was
transferred to a 500 ml Erlenmeyer flask. The sample was diluted to 250 ml with
deionised water. Using a standard solution of 0.1 N sodium hydroxide (Hanns,
analytical grade), the sample was titrated to the end point. The end point was
determined using pH meter and phenolphthalein indicator. 1 ml of phenolphthalein
indicator was added to the sample and titrated to faint pink end point. The volume of
0.1 N sodium hydroxide used was recorded. The total acidity can be calculated using
equation (1)12 and expressed as concentration of citric acid (g/l). The measurement
was repeated at least three times.
% Acid (as anhydrous citric acid) = Volume of 0.1 N NaOH (ml) × 0.64 / 10
(1)
2.5. pH of pineapple juice
pH of pineapple juice samples was evaluated by pH meter Cyberscan 1000
(Eutech Cybernetics, Singapore). The measurement was carried out at least in
triplicates.
2.6. Total soluble solids in pineapple juice
Brix % is generally used as indicator for soluble solid content %. The total
soluble solids of pineapple juice samples were evaluated using digital refractometers
Palette Series (Atago Co. Ltd., Japan).
2.7. Analysis of elemental components in pineapple juice by ICP-MS
The elemental compositions in pineapple juice were determined using Elan
6100 Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) (Perkin Elmer, USA)
method and Multi Element Calibration Standard.
2.8. Organisation of sensory evaluation test
A typical taste panel room is provided with a space between taste panels, so
that they do not influence one another with conversation or facial expressions. The
samples are coded with random letters. Then, the tasters are given an evaluation form.
They are asked to taste one sample at a time, and record their responses. Allow time
between samples so that tasters can record their opinions.
In this test, a 10-trained-members panel were selected to evaluate the quality
of fresh and processed pineapple juice. A 1 to 5 structured scale was used for
sweetness, tartness or sourness, colour and overall acceptability of pineapple juice.
Meanwhile, a 1 to 3 structured scale was used for odour. For sweetness, 1: no, 2: low,
3: fair, 4: strong, 5: very strong; tartness, 1: no, 2: low, 3: fair, 4: strong, 5: very
strong; colour, 1:brown, 2: brownish yellow, 3: slightly brownish yellow, 4: pale
yellow, 5: bright yellow; odour, 1: off-odours, 2: slightly characteristic, 3:
characteristic; overall acceptability, 1: dislikes, 2: dislikes slightly, 3: accepts, 4: likes
slightly, 5: likes very much.
3. Results and discussion
3.1. Effect of electrodialysis on titratable acidity
Titratable acidity was evaluated to determine the total acidity in pineapple
juice. Total acidity is expressed as anhydrous citric acid. Electrodialysis of pineapple
juice resulted in the reduction of titratable acidity in the diluting stream and increment
of titratable acidity in concentrating stream, after two hours of processing. The data
for titratable acidity is tabulated in Table 1.
Table 1
Data for Titratable Acidity
Fresh
Pineapple
Juice
Volume of 0.1 N NaOH (ml)
% Acid (as anhydrous citric
acid)
10.5
0.67
Processed Juice (Using
Electrodialysis)
Diluting
Concentrating
Stream
Stream
9.3
11.3
0.60
0.72
3.2. Effect of electrodialysis on pH of pineapple juice
Electrodialysis of pineapple juice surprisingly decreased the pH value (the
processed juice become more acidic). The pH value reduced from 4.01 to 3.75. It was
expected that the pH value to increase as the conductivity value of pineapple juice
decreased. The conductivity value presented hydrogen ions concentration as well as
citrate ions. In a solution, hydrogen ions determined the degree of acidity. As the
concentration of hydrogen ions were reduced, so it was expected pH value to increase.
This decrease in pH with removal of acidity for the pineapple juice during
electrodialysis was attributed to buffer salts, their ionisation and removal during the
process. Pineapple juice contained weak acids like citric acid and malic acid and
sodium, potassium and calcium salts. The presence of these acids and salts formed a
buffer. During electrodialysis, salts of these acids were transported through the
membranes along with weak acids. This disturbed the buffer action resulting in
reduction of pH along with some removal of acidity5.
If other salts or ions are present in solution besides the conjugate acid-base
pair, the pK′ of the weak acid and hence the pH of the solution will not only depend
on the concentration of conjugate acid-base pair, but also on the concentrations of all
other ions present in solution. Furthermore, divalent ions (e.g. Ca2+) will have a
stronger buffer effect than monovalent ions (e.g. Na+)13.
3.3. Effect of electrodialysis on sugar contents
No significant differences in % Brix value were observed on the
electrodialysed pineapple juice sample. The values in concentrating stream were
slightly higher than in diluting stream. The % Brix varies from 10.17 to 10.50. For
fresh juice, the value was 10.50. After two hours of processing, % Brix in diluting
stream was 10.17 and 10.30 in concentrating stream. As a conclusion, electrodialysis
process did not significantly effect the % Brix value.
Since Brix is a measure of soluble solids (primarily sugars and acids), it
should be expected that Brix in high acid juices should decrease as acid was removed.
But very little of the Brix reading was from acids. Thus, Brix values were essentially
unchanged as the small amount of acid was removed14.
3.4. Effect of electrodialysis on elemental components in pineapple juice
The major elemental components present in pineapple juice are magnesium,
phosphorus and potassium. The other elemental components are present in trace
amount. From pineapple juice elemental analysis, it can be seen that the compositions
of magnesium, phosphorus and potassium were decreased in the diluting stream and
increased in the concentrating stream.
Magnesium (Mg2+), phosphorus (P6+) and potassium (K+) were positive
charged ions. During electrodialysis, the positive charged ions were transported from
the diluting stream to the concentrating stream through cation exchange membranes
towards cathode. As a result the amount of cations in diluting stream was reduced.
Table 2 shows the minerals presents in pineapple juice and their value after
electrodialysis.
Table 2
The compositions of fresh pineapple juice and processed pineapple juice using electrodialysis
Minerals
Zinc (Zn)
Arsenic (As)
Iron (Fe)
Magnesium (Mg)
Sodium (Na)
Phosphorus (P)
Potassium (K)
Aluminium (Al)
Compositions (mg/100 ml)
Fresh Pineapple
Processed Pineapple Juice (Using
Juice
Electrodialysis)
Diluting
Concentrating
Stream
Stream
0.538
0.864
0.586
0.060
0.090
0.092
0.748
1.238
0.982
12.004
11.538
13.478
0.898
2.836
3.402
9.250
9.070
9.756
128.076
111.538
159.722
0.890
1.320
0.866
Sensorial Analyses of Pineapple Juice
When it comes to consumer quality acceptance, there is still no substitute for
sensory evaluation. The sensory evaluation test was done to determine the quality and
consumer acceptance of the treated pineapple juice using electrodialysis. The scales
and categories test was used. The results of the sensory evaluation test are tabulated in
Table 3.
Table 3
Sensory Evaluation Test Results
Pineapple
Characteristics
Sweetness
Tartness
Colour
Odour
Overall
Acceptability
Average Score
Percentage (%)
Sample M
Sample S
Sample M
Sample S
2.5
4.1
4.5
2.6
2.8
3.1
2.9
4.2
2.5
3.3
50.0
82.0
90.0
86.7
56.0
62.0
58.0
84.0
83.3
66.0
Sample M: Fresh pineapple juice
Sample S: Processed pineapple juice (deacidification using electrodialysis)
The average score by the taste panellists showed a low to fair sweetness in
fresh juice and a fair sweetness in processed juice. They also found out strong tartness
in fresh juice and nearly fair tartness in processed juice. For colour, no significant
differences were noticed as the colour of the two samples was in the range of pale
yellow to bright yellow. A slightly characteristic to characteristic, was found in odour
analysis of both samples. On the whole, the taste panellists accept the electrodialysed
juice better.
4. Conclusion
The results from chemical composition and sensory analysis of deacidified
pineapple juice shows a more acceptable level compared to fresh pineapple juice.
Acknowledgement
The authors wish to thank The Ministry of Science, Technology and
Environment for Intensified Research in Priority Area (IRPA) Grant Vote 72101.
References
[1] Arthey, D. (1995). Food Industries Manual. In: Fruit and Vegetable Product.
London. 151.
[2] Bartolomé, A. P., Rupérez, P. and Fúster, C. (1995). Pineapple Fruit:
Morphological Characteristics, Chemical Composition and Sensory Analysis of Red
Spanish and Smooth Cayenne Cultivars. Food Chemistry. 53: 75 - 79.
[3] Duke, J. A. (1983). Ananas comosus (L.) Merr. Handbook of Energy Crops.
unpublished.
[4] Samson, J. A. (1986). Tropical Fruits. 2nd ed. New York: Longman Inc.
[5] Adhikary, S. K., Harkare, W. P., Govindan, K. P., Chikkappaji, K. C., Saroja, S.
and Nanjundaswamy, A. M. (1987). Deacidification of Fruit Juices by Electrodialysis
- Part II. Indian Journal of Technology. 25: 24 - 27.
[6] Vibhakar, S. W., Prabhakar, J. V. and Bhatnagar, H. C. (1966). Journal Science
Food Agriculture. 17: 488.
[7] Carneiro, L., Iralla dos Santos Sa, Flávia dos Santos Gomes, Matta, V. M. and
Cabral, L. M. C. (2002). Cold Sterilization and Clarification of Pineapple Juice by
Tangential Microfiltration. Desalination. 148: 93 - 98.
[8] Bazinet, L., Lamarche, F. and Ippersiel, D. (1998). Bipolar-membrane
Electrodialysis: Applications of Electrodialysis in the Food Industry. Trends in Food
Science and Technology. 9: 107 - 113.
[9] Strathmann, H. (1992). Electrodialysis. In: Winston Ho, W. S. and Sirkar, K.K.
eds. Membrane Handbook. New York: Van Nostrand Reinhold. 218 - 262.
[10] Strathmann, H. (1981). Membrane Separation Processes. Journal of Membrane
Science. 9: 121 - 189.
[11] Sreenath, H. K., Sudarshanakrisna, K. R. and Santhanam, K. (1994).
Improvement of Juice Recovery from Pineapple Pulp or Residue Using Cellulases and
Pectinases. Journal of Fermentation and Bioengineering. 78(6): 486 - 488.
[12] U. S. Customs Laboratory Methods. Fruit Juices and Fruit Syrups. United States,
USCL 20-08.
[13] Horner, R. D. (1997). Biochemistry Laboratory. Johns Hopkins University.
[14] Couture, R. and Rouseff, R. (1992). Debittering and Deacidifying Sour Orange
(Citrus aurantium) Juice Using Neutral and Anion Exchange Resins. Journal of Food
Science. 57(2): 380 - 384.